Update free-programming-playgrounds.md (#9498)

* Update free-programming-playgrounds.md

* Update free-programming-playgrounds.md

alphabetize

* Update free-programming-playgrounds.md

alphabetize

* fix titles

* fix R order

---------

Co-authored-by: Eric Hellman <eric@hellman.net>

more/free-programming-playgrounds.md

@@ -95,6 +95,7 @@
 * [Compiler Explorer](https://godbolt.org)
 * [InterviewBit](https://www.interviewbit.com/online-cpp-compiler/)
 * [LabStack](https://code.labstack.com/cpp)
+* [Online C++ Compiler](https://www.codinguru.online/compiler/cpp)
 * [OnlineGDB](https://www.onlinegdb.com/online_c++_compiler)
 * [SoloLearn](https://code.sololearn.com/cpp)
 
@@ -156,6 +157,7 @@
 
 ### Go
 
+* [GO Lang Compiler](https://www.codinguru.online/compiler/go)
 * [Go Playground](https://play.golang.org)
 * [SoloLearn](https://code.sololearn.com/go)
 
@@ -178,6 +180,7 @@
 * [Flexbox Froggy](https://flexboxfroggy.com) - Codepip
 * [Flexy Boxes](https://the-echoplex.net/flexyboxes/)
 * [Grid Garden](https://cssgridgarden.com) - Codepip
+* [HTML, CSS, JavaScript](https://www.codinguru.online/compiler/html)
 * [Learn advanced html and css](https://www.theodinproject.com/paths/full-stack-javascript/courses/advanced-html-and-css) - The Odin Project
 * [Learn Intermediate html and css](https://www.theodinproject.com/paths/full-stack-javascript/courses/intermediate-html-and-css) - The Odin Project
 * [LiveCode](https://livecodes.io) - LiveCode
@@ -193,6 +196,7 @@
 ### Java
 
 * [InterviewBit - Online Java Compiler IDE](https://www.interviewbit.com/online-java-compiler/)
+* [Java Compiler](https://www.codinguru.online/compiler/java)
 * [JDoodle - Online Java Compiler Advanced IDE](https://www.jdoodle.com/online-java-compiler-ide/)
 * [JDoodle - Online Java Compiler IDE](https://www.jdoodle.com/online-java-compiler/)
 * [OnlineGDB](https://www.onlinegdb.com/online_java_compiler)
@@ -210,6 +214,7 @@
 * [Grasshopper](https://grasshopper.app) *(Google account required)*
 * [Hello Website - (Glitch)](https://glitch.new/website) *(Account requested, not required)*
 * [InterviewBit - Online JavaScript Compiler IDE](https://www.interviewbit.com/online-javascript-compiler/)
+* [JavaScript Compiler](https://www.codinguru.online/compiler/javascript)
 * [JSBin](https://jsbin.com)
 * [JSFiddle](https://jsfiddle.net)
 * [Liveweave](https://liveweave.com) - Amit Sen
@@ -238,6 +243,11 @@
 * [Play with Kubernetes](https://labs.play-with-k8s.com)
 
 
+### Markdown
+
+* [Markdown Editor](https://www.codinguru.online/compiler/markdown)
+
+
 ### Multiple Languages
 
 * [CodeChef](https://www.codechef.com/ide)
@@ -276,6 +286,7 @@
 
 * [Codepad](http://codepad.org/?lang=PHP)
 * [ExtendsClass](https://extendsclass.com/php.html)
+* [PHP Online Compiler](https://www.codinguru.online/compiler/php)
 * [PHPTester](http://phptester.net)
 * [SoloLearn](https://code.sololearn.com/php)
 
@@ -287,6 +298,7 @@
 * [OnlineGDB](https://www.onlinegdb.com/online_python_compiler)
 * [Programiz.com](https://www.programiz.com/python-programming/online-compiler/)
 * [Pynative.com](https://pynative.com/online-python-code-editor-to-execute-python-code/)
+* [Python Online Compilers](https://www.codinguru.online/compiler/python)
 * [Python Trinket](https://trinket.io/python)
 * [Python Tutor](https://pythontutor.com)
 * [Python.org Shell](https://www.python.org/shell)
@@ -299,6 +311,7 @@
 
 * [myCompiler](https://www.mycompiler.io/online-r-compiler)
 * [R-Fiddle](http://www.r-fiddle.org)
+* [R Online Editors](https://www.codinguru.online/compiler/R)
 * [Rextester](https://rextester.com/l/r_online_compiler)
 * [SoloLearn](https://code.sololearn.com/r)
 
@@ -403,3 +416,4 @@
 
 * [Vim Adventure](https://vim-adventures.com) - Doron Linder
 * [Vim Genius](http://vimgenius.com) - Vic Ramon, Rye Mason
+